Stereology in Grading and Prognosis of Canine Cutaneous Mast Cell Tumors

Abstract

Canine cutaneous mast cell tumors (ccMCTs) are currently graded according to Patnaik and Kiupel grading schemes. The qualitative and semiquantitative parameters applied in these schemes may lead to inter- and intraobserver variability. This study investigates the prognostic value of volume-weighted mean nuclear volume ($\overline{v_v}$), a stereological estimation that provides information about nuclear size and its variability. $\overline{v_v}$ of 55 ccMCTs was estimated using the "point-sampled intercept" method and compared with histological grade and clinical outcome. The clinical history of dogs treated with surgical excision alone was available for 30 ccMCTs. Statistical differences in $\overline{v_v}$ were found between grade II ($\overline{x}$= 115 ± 29 µm³) and grade III ccMCTs ($\overline{x}$= 197 ± 63 µm³), as well as between low-grade ($\overline{x}$= 113 ± 28 µm³) and high-grade ccMCTs ($\overline{x}$= 184 ± 63 µm³). An optimal cutoff value of $\overline{v_v}$ ≥ 150 µm³ and $\overline{v_v}$ ≥ 140 µm³ was determined for grade III and high-grade ccMCTs, respectively. In terms of prognosis, $\overline{v_v}$ was not able to predict the clinical outcome in 42% of the cases; however, cases with $\overline{v_v}$<125 µm³ had a favorable outcome. These results indicate that, despite having limited prognostic value when used as a solitary parameter, $\overline{v_v}$ is highly reproducible and is associated with histological grade as well as with benign behavior.

Keywords: dogs; histological grading; mast cell tumor; mean nuclear volume; prognosis; skin; stereology; surgical pathology.